The present invention relates generally to intravascular catheter systems that utilize thermal sensors to locate and map hot spots of the atherosclerotic plaque, vascular lesions, and aneurysms in human vessels. Vulnerable plaques consist of a lipid-rich core and inflammatory cells, and these plaques are prone to rupture and erosion. Evidences indicate that plaque rupture triggers 60 to 70% of fatal myocardial infarctions. In a further 25 to 30% of fatal infarctions, plaque erosion or ulceration is the trigger. In plaque erosion, the endothelium beneath the thrombus is replaced by inflammatory cells. These inflammatory cells are associated with plaque rupture and ulceration. Both may respond to and aggravate intimal injury, promoting thrombosis and vasoconstriction.
These vulnerable plaques are often angiographically invisible. These vulnerable plaques are at a significant risk of precipitating infarction, and the majority of these plaques occur in coronary arteries that were apparently normal or only mildly stenotic on the previous angiograms. S. Ward Casscells et al have shown that plaques with a significant number of inflammatory cells and a lipid-rich core might be identifiable by the heat associated with the inflammatory process.
Intravascular ultrasonography has recently become an important diagnostic tool which allows direct visualization of plaque morphology and distribution. By way of example, Yock, U.S. Pat. No. 4,794,931, U.S. Pat. No. 5,000,185, and U.S. Pat. No. 5,313,949, and Maroney et al., U.S. Pat. No. 5,373,849 describe methods and catheters for performing intravascular ultrasonography. However, intravascular ultrasonography cannot give information on inflammatory cellular content, and is not capable of detecting temperature increase in the composition of the plaque, which is believed to be a criteria of imminent arterial thrombosis. The composition of the vulnerable plaque, particularly the presence of a large lipid core with the associated inflammatory cells, is the most powerful predictor of plaque rupture with the associated events of thrombosis and infarction.
It would be desirable then to provide a catheter which can detect and map temperature variations in the atherosclerotic plaque and on the plaque surface. These parameters can be integrated with an ultrasound catheter that can scan a plane normal to the catheters axis or distal of the catheter itself. Being able to see an increase in vulnerable plaque temperature as well as visualize the area at risk would be of great benefit to the physician, in terms of predicting potential thrombus formation/infarction and administering therapeutic intervention.
Additionally, by way of example, Klein et al., U.S. Pat. No. 5,279,565, Kaplan et al., U.S. Pat. No. 5,336,178, and Onishi et al., U.S. Pat. No. 5,547,472 describe methods and catheters for intravascular localized drug delivery. It is postulated that deliver of anti-inflammatory and antithrombotic agents directly, or adjacent to plaques at risk would reduce the likelihood of plaque rupture or ulceration and the formation of thrombus. However, at the present time these catheters are only capable of delivering the agents to angiographically identifiable plaques, and these catheters cannot distinguish vulnerable plaques from simple plaque which is not at risk of thrombosis. It would be desirable then to provide a catheter that can discriminate the stated plaque characteristics and pin point the exact delivery site, utilizing the thermal and/or ultrasonic visualization.